Fix Mutant::Loader to use correct constant scope

* Do not load the compiled code before CompiledCode#create_script
  was called.
* Add a test case that illustrates the issue.

lib/mutant/loader.rb

@@ -25,16 +25,22 @@ module Mutant
     #
     def initialize(root)
       @root = Helper.deep_clone(root)
-      Rubinius.run_script(compiled_code)
+      Rubinius.run_script(script.compiled_code)
+    end
+
+    # Return code script
+    #
+    # @return [Rubinisu::CompiledCode::Script]
+    #
+    # @api private
+    #
+    def script
+      compiled_code.create_script
     end
 
     # Return compiled code for node
     #
-    # This method actually returns a Rubnius::CompiledMethod
-    # instance. But it is named on the future name of CompiledMethod
-    # that will be renamed to Rubinius::CompiledCode.
-    #
-    # @return [Rubinius::CompiledMethod]
+    # @return [Rubinius::CompiledCode]
     #
     # @api private
     #

spec/unit/mutant/loader/class_methods/load_spec.rb

@@ -1,7 +0,0 @@
-require 'spec_helper'
-
-describe Mutant::Loader, '.load' do
-  subject { object.load(node) }
-
-  let(:object) { described_class }
-end

spec/unit/mutant/loader/class_methods/run_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe Mutant::Loader, '.run' do
+  subject { object.run(node) }
+
+  let(:object) { described_class }
+
+  after do
+    Object.send(:remove_const, :SomeNamespace)
+  end
+
+  let(:source) do
+    # This test case will blow up when not executed
+    # under toplevel binding.
+    <<-RUBY
+      class SomeNamespace
+        class Bar
+        end
+
+        class SomeOther
+          class Foo < Bar
+          end
+        end
+      end
+    RUBY
+  end
+
+  let(:node) do
+    Rubinius::AST::Script.new(source.to_ast).tap do |source|
+      source.file = "/some/source"
+    end
+  end
+
+  it 'should load nodes into vm' do
+    subject
+    SomeNamespace::SomeOther::Foo
+  end
+end